1. Field of the Invention
This invention relates to a laser irradiation apparatus and a laser irradiation method for irradiating linear laser light on an irradiation object, and further relates to a fabrication method for a thin film semiconductor device and a fabrication method for a display apparatus for crystallizing a semiconductor film by irradiating linear laser light.
2. Description of the Related Art
In recent years, a thin film transistor (hereinafter referred to simply as TFT) for which a crystalline semiconductor film represented by a polycrystalline silicon film is used as a device for forming a driving circuit for controlling pixels or a switching device for pixels for a display apparatus such as a liquid crystal display apparatus, an organic EL (Electro Luminescence) display apparatus and so forth.
As a method for crystallizing an amorphous semiconductor film such as an amorphous silicon film, a method which uses laser light (laser beam) is known and disclosed, for example, in Japanese Patent Laid-Open No. 2001-156017. In this method, linear laser light is irradiated on an amorphous semiconductor film using a laser irradiation apparatus to heat the semiconductor film so as to be crystallized. Normally, the laser light used for the crystallization is pulse laser light, and by the semiconductor film is momentarily heated by the pulse laser light so as to be crystallized to obtain a crystalline semiconductor film.
FIGS. 5A and 5B schematically show an example of a configuration of an existing laser irradiation apparatus. Refer to FIGS. 5A and 5B, the laser irradiation apparatus includes an optical system 51, a pair of cutting members 52 and a table 53.
The optical system 51 forms laser light outputted from a laser light source not shown so as to have a linear cross section (cross section perpendicular to an optical axis). The cutting members 52 cut the laser light (linear beam) LB formed so as to have a linear form by the optical system 51 in a predetermined length in an X direction along a line longitudinal direction of the laser light LB, which is a left and right direction in FIG. 5.
The table 53 supports a substrate 54 on which a semiconductor film which is an irradiation object is formed. On a main face (top face) of the substrate 54, an amorphous semiconductor film 55 is formed at a stage before laser irradiation. Further, the table 53 is supported for movement by a table moving mechanism not shown.
In order to crystallize the semiconductor film 55 in a laser light irradiation target region 56 using the laser irradiation apparatus having the configuration described above, the substrate 54, on which the semiconductor film 55 which is the irradiation object is placed, is placed on the table 53 so as to be supported by the table 53. Then, the cross sectional shape of the laser light outputted from the laser light source not shown is converted into a linear form by the optical system 51, and then the linear laser light LB is irradiated from the optical system 51 on the substrate 54. At this time, part of the linear laser light LB, that is, the opposite end portions of the linear laser light LB, are block by the cutting members 52 to cut the laser light LB so as to have a predetermined length conforming to the size of the laser light irradiation target region 56 of the substrate 54.
Further, in order to irradiate the laser light on a wide area on the substrate 54, the table 53 is successively moved in a Y-direction at a fixed pitch in synchronism with a timing at which the laser light LB is irradiated. As a result, the semiconductor film 55 is crystallized by irradiation of the laser light LB.